Unloader for circular silos



Jan. 24, 1961 H. c. LMILLEgQ Em 2,969,156

UNLOADER FOR CIRCULAR SILOS Filed May 9, 1956 6 Sheets-Sheet 1 mvmoxs; V 1 fie/vv c L. MILLER Jan. 24, 1961 H. c. L. MILLER El'AL UNLOADER FOR CIRCULAR SILOS Filed May 9, 1956 6 Sheets-Sheet 2 HENRY C. L. Mama 6-; JaEL lD/q TK/Ns INVENTORS.

Jan. 24, 1961 H. c. L. MILLER ETAL 2,969,156

UNLOADER FOR CIRCULAR sxLos Filed May 9. 1956 1 6 Sheets-Sheet 3 INVENTORS HEN Y cL. Mme JOE/.MWATKINS,

ATTORNEY Jan. 24, 1961 H. c. MILLER ETAL 2,969,156

UNLOADER FOR CIRCULAR SILOS Filed May 9, 1956 6 Sheets-Sheet 4' /3z f/EA/FY C. L. MILLER 5 JOEL MW: rK/Ns,

BY W

ATTORNEY IN VENTORS Jan. 24, 1961 H. c. L. MILLER ETAL 2,969,156

UNLOADER FOR CIRCULAR SILOS 1 Filed May 9, 1956 6 Sheets-Sheet 5 ATTORNEY Jan. 24,1961 H. c. MILLER ETAL 7 2,969,156

UNLOADER FOR CIRCULAR SILOS Filed May 9, 1956 6 Sheets-Sheet I I 22s h -220 0 224 IN V EN TOR. HENRY C.L. MILLER A KINS %L B W T A TTORNE) UNLOADER FOR CIRCULAR SILOS Henry C. L. Miller, Richmond, Va., and Joel H. Watkins, Bay City, Mich.; said Watkins assignor to Miller Holit, Inc., Richmond, Va., a corporation of Delaware Filed May 9, 1956, Ser. No. 583,790

2 Claims. (Cl. 214-17) This is a continuation in part of our copending application Serial No. 385,404 filed October 12, 1953, now abandoned.

It is an object of this invention to provide means for unloading non-freeflowing material from cylindrical storage bins of very large capacity, say from 15,000 cubic feet to 100,000 cubic feet. This is important for the storage of such commodities as bark and particularly wood chips intended to be used in the manufacture of wood pulp. v

The paper making process is essentially continuous but it is made up of many distinct units. To, name a few of the more important, there is the wood room, the digester room, the preparation room and the actual paper machine. Each of the operations represented thereby must have storage accommodations between it and the next operation, so that a temporary shut-down of any one operation does not necessitate the shut-down of all other operations.

Until the last few years, chips were stored in large bins rising above the top of the digesters, which meant that the entire tonnage of chips had to be elevated to the highest point in the mill and this entire tonnage had to be supported on the tallest columns. Power cost, incident to the elevation was high and construction cost relative to the supports also was high.

In later years, the tendency in plant design has bee to store chips coming from the chip screens, at or about ground level and to elevate the chips by means of conveyors only to a height sufiiciently above the upper ends of the digesters to permit gravity-charging of the digesters.

Chips as they come from the chip screens are not at all freeflowing and have pronounced arching and caking properties. The angle of slip is high and it would be altogether. impossible to empty a large bin through a central opening in a conical bottom. Numerous rectangular bins have been devised-and some excellent equipment is available for unloading these. However, as the mills have become larger, the demand is for larger bins of the size and the type herein contemplated. Bins of the old rectangular type become excessive in cost, both from the standpoint of construction and because of the necessity of having the bin loading mechanism traverse the length of the bin.

A cylindrical bin, on the other hand, has maximum cubic capacity for a minimum of surface area and can be loaded by a single fixed conveyor delivering tothe top center of the bin. 7

Among the objects of this invention is the provision of means for unloading a cylindrical bin in which the unloading means traverses the entire area of the cylindrical bottom and in which it is unnecessary to resort to a conical bottom in order to secure flow of the chips.

It is a further object of this invention to provide means i for unloading a cylindrical bin in which the unloading means so agitate the bottom of the body of chips as to prevent caking and arching.

nited States Patent It is a further object of this invention to provide an adjustable ratio of speed of the unloading means and speed of the traverse. I

It is a further object of this invention to provide means to accommodate for temporary interruption of the traverse while continuing operation of the unloading means during such interruption.

The above and other objects will be made clear from the following detailed description taken in connection with the annexed drawings in which:

Fig. 1 is an elevation, partly in section, of a bin and one version of the improved unloading devices;

Fig. 2 is an enlarged view of the unloader driving means;

Fig. 3 is a top plan view of the unloader driving means;

Fig. 4 is an elevation partly in section of a modified form of the invention;

Fig. 5 is a side elevation, partly in section, of a modified form of bin;

Fig. 6 is an enlarged view of the drive of Fig. 5;

Fig. 7 is an elevation, partly in section, of a modified form of bin;

Fig-.8 is a detailed illustration of an alternative arrangement of rack and pinion;

Fig. 9 is a plan view of a preferred form of drive;

Fig. 10 is an elevation of Fig. 9;

Fig. 11 is a detail of mechanism alternative to that of Figs. 9 and 10; and

Fig. 12 is a plan view on the line 1212 of Fig. 11. Referring now to Figs. 1, 2 and 3, there is shown a cylindrical bin or silo 10 formed of concrete staves supported by circumferential tie rods 12. The bin has an inwardly sloping concrete floor 14 and a short conical portion 16, guiding chips from the cylindrical portion of the bin to the concrete floor 14.

At the center of the floor 14, a steel thimble 18 is secured to a cast iron ring 20 which bears on a steel ring 22, which steel ring 22 is supported by the concrete floor 14. This provides a bearing on which the thimble 18 may rotate. A plate 24 is secured near the top of the thimble 18 and supports a bearing 26. Another bearing 28 is secured to the vertical wall of the thimble 18 in alignment with the bearing 26. A shaft 30 extends radially of the bin 10 and has one end supported in bearings 26 and 28, while its outer end is supported in a bearing 32. A tapered screw 34 is formed on the shaft 30 which is rotated in a direction to advance chips radially into the thimble 18, where the chips drop through a chute 36 onto a conveyor 38. While a tapered screw as shown is preferred, it would be no departure from the invention to use either a straight screw or a vertical pitch screw.

The bearing 32 is supported by a frame 40 on a carriage 42, which in turn is supported by wheels 44 on rails 46. These rails are circular and concentric with the bin 10.

A motor 48 is mounted on the carriage 40 and derives power from circular busses 62 by trolley 49. The motor 48 drives through a speed-reducer 50, which through one sprocket 52 (Fig. 4) drives the screw 34 and through a second sprocket 54 drives a speed-reducer 56, which in turn drives a pinion 58. The pinion 58 meshes with a circular rack 60 which is concentric with the bin 10. If desired, the pinion 58 may be connected to the speedreducer 56 through a friction connection. 7

In operation, the motor 48 drives both the screw 34 and the pinion 58 so that the carriage 40 is driven round and round the base of the bin 10 while simultaneously at all times the screw 34 is rotating on its axis and delivering chips radially inwardly to the chute 36.

If the screw 34 encounters an obstacle to its rotation around the bottom of the bin, the friction connection be,

tween the pinion 58 and the speed-reducer 56 will permit such rotation to be interrupted. The rotation of the screw on its own axis, however, keeps up so that it literally cuts its way through any obstacles. Clearly, any tendency toward caking and arching is thereby eliminated.

Referring now t Pig. 5 and .Fig. 6 there is shown a polygonal bin 100 made up of steel panels 182. The bin is loaded by a conveyor 104, which delivers chips above the center of the bin. Bin 108 is suspended from columns 106 by means of struts 18 8. A substantially flat floor 110 is made up of plates 112 and has in its center a thimble 114 mounted to rotate in a bearing 116.

The thimble 114 has in its upper portion a plate 118 (Fig. 6) which supports a bearing 120, a second bearing 1-22 is mounted in a wall of the thimble. A shaft 124 is supported at one end by the bearings 1'28 and 122 and at its other end is supported in a bearing 126. A tapered screw 128 is formed on the shaft 124 and is rotated to direct chips into the thimble 114, whence through a chute 130, they descend to a conveyor 132.

A rigid coupling 134 connects the shaft 124 to a speed-reducer 136 driven by a motor 138. The motor 138 is mounted on a carriage 140 which is supported by wheels 1 42 which bear on a mono-rail 144, which is concentric with the bin 100. The speed-reducer 136 drives a second speed-reducer 146 which in turns drives a pinion 148. The pinion 148 meshes with a circular rack also concentric with the bin 100. A friction clutch is inserted between the speed-reducers 126 and 146 whereby to permit interruption of the rotary movement around the base of the bin of the screw 128 while continuing rotation of the screw 128 about its own axis.

Fig. 7 shows a variation of the form of Fig. l in which the sloping portion 16 has been omitted and the vertical walls approach the substantially flat bottom 16. The same reference numerals as in Fig. 1, et seq., are used to identify the active parts in Fig. 7.

Fig. 8 shows a different relationship of rack and pinion applicable to any of the forms heretofore discussed. It is clear that the action of a screw such as 128 of Fig. 5 will exert a considerable radial thrust in an outward direction. Usually this Will be taken by the thimble 114 by proper arrangement of bearings 122 and 128. If, how ever, it is desired to relieve the thimble of all or part of this loading, then as in Fig. 8 a pinion 148' driven by a speed-reducer will mesh with an external curved rack 150'. In this arrangement, the rack rather than the thimble resists the outward thrust.

The friction clutch previously mentioned for relief of the traversing drive is subject to the wear and consequent maintenance of all such friction relief devices. it has been found that the ratio between the rotary speed of the axis of the screw about the axis of the silo is critical. Moreover, this ratio, for optimum performance varies widely for various contents of the silo, e.g.: chips, bark, etc. In the interest of standardization, therefore, it is most desirable to provide a simple, easy to make adjustment of this ratio. It is further desirable to substitute resilient relief for the friction relief above mentioned.

Referring now to Figs. 9 and 10, there is shown a carriage 200 similar to the carriage 42 of Figs. 1, 2 and 3. On the carriage 200 is mounted a motor 282 which through a flexible coupling 204, drives a single speedreducer 286. The output shaft 288 of the speed-reducer 286 has mounted at its free end a sprocket .210 which, through a chain 212 drives a sprocket 214 on the shaft 216 of an unloading screw 218.

On the end of the shaft 216 opposite the screw 218 is fixed an adjustable excentric 220. This is adjustable from a minimum of zero throw to a predetermined maximum. A connecting rod 222 has one end pivotally secured to the excentric 220 and its other end pivotally secured to a lever 224. The rod 222 is actually a telescoping rod in sleeve with one-way spring relief permitting relative sliding between the rod and the sleeve.

The lever 224 engages, at its opposite end, one member of a friction ratchet 226, the other member of which is secured to a shaft 228. On the shaft 228 is secured a gear or sprocket 230 which engages an annular gear or chain 232 secured to the machine bed.

-As the shaft 216 rotates, so does the screw 218. For each revolution of the shaft 216, the excentric 228, through the connecting rod 222 causes a complete oscillation of the lever 224 which because of the ratchet 226 produces only one half a revolution of the shaft 228 and its gear or sprocket 130. On the return half of the oscillation, the shaft 228 remains stationary.

The load on the screw 218 tends to thrust the carriage 200 in a direction opposite to the direction of its traverse as enforced by the gear or sprocket 238. To meet this condition, the shaft 228 is provided with a second friction ratchet 234 having one of its members fixed and being oppositely directed to friction ratchet 226. This prevents regression of the carriage during the return stroke of the lever 224.

The spring relief in the connecting rod 222 prevents traverse of the carriage 200 when the screw 218 meets exceptional resistance to the traversing action.

The rotary speed of screw 218 is many times the rotary speed of the carriage around the axis of the silo. The extreme minimal capacity of the excentric 220, however, permits the establishment of extreme rotary speed ratios with the use of only one speed-reducer 206.

The minimum throw of the excentric 220 is zero, and various conditions of space and engineering requirements may limit its maximum throw and therefore the range of adjustment of the ratio of rotary speeds. Figs. 11 and 12 illustrate an expedient for doubling the range of adjustment for any maximum throw of the excentric. These figures show an excentric 200 on a shaft 216. Riding on the excentric 200 is a composite rod designated generally as 250. This is made up of rod section 252 secured to a sleeve section 254 which has an annular end flange 256. A second rod section 258 has one end inside the sleeve 254 and is slidable through the flange 256. A flange 260 is secured to this end of the rod 258 and is slidable in the sleeve 254. A spring 262 surrounds this portion of the rod 258 and is compressed between the flanges 256 and 260.

Spaced from the flange 256, there is secured to rod 258 another flange 264. A second spring 266 surrounds this portion of the rod 258 and is compressible between the flanges 264 and 256.

The extremity of rod 258 terminates in a pair of opposed racks 268 and 270. These racks are parallel and mutually opposed, as best seen in Fig. 12. The rack 268 engages a pinion 272 while the rack 270 engages a pinion 274. Each pinion forms one member of a friction ratchet for driving a shaft 276 to which a gear or sprocket is mounted for the purpose of advancing the carriage.

Rotation of the, excentric 200 on the shaft 216 will reciprocate the rod 252 and through the springs 262 and 266 will reciprocate the rod 258 and the racks 268 and 270. On a forward stroke, one of the racks will cause its pinion'to override its friction clutch, while the other rack causes its pinion to engage its friction clutch to rotate the shaft 276 and thereby advance the carriage. On the return stroke, the last named rack causes its pinion to override its friction ratchet while the first named rack causes its pinion to engage its friction ratchet to rotate shaft 276 to advance the carriage in the same direction. The spring 266 offers relief to over resistance in one direction while the spring 262 offers relief against obstruction in the opposite direction.

It is clear that the arrangement of Figs. 11 and 12 doubles the advance of the carriage for each revolution of the excentric for any given throw. This in itself is not particularly important, since in any case the traverse of the carriage is very slow. The importance of the arrangement of Figs. l1 and 12 lies in the fact that it doubles the maximum a ljustment of traverse from zero to the maximum adjustment of the throw of the excentric.

While certain specific constructions have been disclosed herein, the invention is not to be limited to the details of such construction but only as set forth in the subjoined claims.

We claim:

1. Apparatus for unloading a bin which is generally concentric about a vertical axis comprising a radially directed screw conveyor adjacent the bottom of the bin,

a carriage mounted on a track adjacent the periphery' of the bin, 2. motor mounted on said carriage, bearings mounted on said carriage to receive and guide the outer end of said conveyor, means mounted on said carriage for driving the same around said track, means connecting said motor to said conveyor for rotating the same about its axis and means connecting said motor to said driving means for driving said carriage around said track, said last named means including an adjustable eccentric on 6 the shaft of said conveyor, a spring relieved connecting rod having one end connected to the throw of said eccentric and means at the other end of said connecting rod for actuating said drive.

2. Apparatus according to claim 1 in which the means for actuating said drive comprises: a shaft, a ratchet clutch to drive said shaft in one direction, a lever to actuate said ratchet, the free end of said lever being pivoted to said connecting rod, and a second ratchet, oppositely directed, to prevent reverse movement of said shaft.

References Cited in the file of this patent UNITED STATES PATENTS 1,275,558 Holmgreen Aug. 13, 1918 2,598,388 Hurter May 27, 1952 FOREIGN PATENTS 71,584 Sweden Apr. 7, 1931 201,148 Switzerland Feb. 1, 1939 

